1. Field of the Invention
The present invention relates to an optical information recording medium provided with an optically detectable information recording layer, the producing method thereof and a method of recording/erasing/reproducing information.
2. Description of the Prior Art
A recording material thin film layer comprising a metal thin film and an organic thin film is formed on a disc-shaped or a card-shaped substrate. A high energy beam focused on a micro light spot having a submicron order diameter is irradiated onto the recording material layer, thereby a local variation is generated on recording material layer. Thereby, such a technique so that an information signal is stored is already well known. More specifically, when an optical magnetic material thin film and a phase change material thin film are used for a recording layer, it is easy to rewrite the signal. Accordingly, this technique has been actively studied and developed. For example, in case of the optical magnetic recording medium, a difference of a rotating angle on a polarized surface of a reflected light generated due to the difference of a magnetization state is used as the record. Furthermore, in case of the phase change recording medium, an amount of a reflected light relative to a light having a specific wavelength in a crystalline state is different from that in an amorphous state, thereby the difference is used as the record. A laser output is modulated between a record level having a relatively higher power and an erasure level having a relatively lower power, and the modulated output is only irradiated on a recording medium. Thereby similarly to a magnetic disk, there is such a characteristic that the record erasure and the record of a new signal can be simultaneously performed (it is possible to overwrite the record). The information signal can be rewritten for a short time.
Usually, the optical magnetic recording medium and the phase change recording medium comprise, for example, a multi-layer film shown in FIG. 1. That is, on a substrate 1 comprising a resin plate of a polycarbonate and PMMA (polymethyl-methacrylate), a glass plate, or the like, usually, a recording layer 3 having an optical absorption comprising the phase change material and the optical magnetic material inserted between protective layers 2 and 4 comprising a dielectric material is formed. Furthermore, a metallic reflecting layer 5 comprising an alloy of Au and Al for increasing an optical absorption efficiency on the recording layer 3 and for acting as a thermal diffusion layer is formed on the protective layer 4. These layers are sequentially laminated by a sputtering method, a vacuum deposition method, or the like. Furthermore, an overcoat layer 6 is formed on an uppermost layer in such a manner that a scratch and dusts are not attached to these layers. Usually, a laser beam is incident from a side of the substrate 1. In many cases, a front surface of the substrate 1 is provided with a concave-convex groove track or a concave-convex pit sequence as guide means for guiding the laser beam to a predetermined position on the disk.
A function of each layer and a concrete example of materials forming each layer are as follows.
In case of the recording layer 3, when the phase change material is used, chalcogenite thin film whose base comprises Te and Se, for example, a Gexe2x80x94Sbxe2x80x94Te alloy thin film, a Gexe2x80x94Sbxe2x80x94Texe2x80x94Se alloy thin film, an Inxe2x80x94Sbxe2x80x94Te alloy thin film, an Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te alloy thin film, an Inxe2x80x94Se alloy thin film, and the like are reported. In the medium using such phase change materials, the laser beam is irradiated, thereby the signal is recorded and reproduced. As already described, while the power of the laser beam is being modulated at a strong level and a weak level, the laser beam is irradiated onto a revolving recording medium. A portion irradiated with the strong power is locally melt in an instant, thenceforth, the portion is quenched. Thereby the portion is amorphized, and the signal is recorded. Furthermore, at the portion irradiated with a relatively weak power, the amorphous-state portion is annealed, thereby the portion is crystallized, and the recorded signal is erased. In order to reproduce the signal, the power of the laser beam is reduced enough in such a manner that the recording film is not changed, and the laser beam is irradiated. At this time, a strength of the reflected light is detected, and whether the portion irradiated with the laser beam is in the crystalline state or the amorphous state is judged, thereby the signal is reproduced.
The functions of the protective layers 2 and 4 comprising a dielectric material are, for example, as follows:
1) the recording layer is protected from an external mechanical damage;
2) a thermal damage such as a roughness on the surface of the substrate, a break of the recording layer and an evaporation, etc. occurred due to repeatedly rewriting the signal are reduced, thereby a repetition of rewriting the signal can be increased;
3) an interference effect of a multipath reflection is used so that an optical change can be enhanced;
4) an influence from an outside air is intercepted so that a chemical change can be prevented.
As the material comprising the protective layer for satisfying the above objects, heretofore, an oxide such as SiO2, Al2O3 or the like, a nitride such as Si3N4, AlN or the like, an acid nitride such as Sixe2x80x94Oxe2x80x94N or the like (for example, disclosed in Japanese Patent Application Laid-open No. 3-104038), a sulfide such as ZnS or the like, a carbide such as SiC or the like, or a mixed material such as ZnSxe2x80x94SiO2 or the like (disclosed in Japanese Patent Application Laid-open No. 63-103453) is proposed, and one part of them is practically used.
Two layers are provided to the protective layer, thereby the characteristic thereof can be enhanced. The example of the phase change recording medium is disclosed in Japanese Patent Application Laid-open No. 5-217211. That is, the dielectric layer comprising the nitride (SiN, AlN) and the carbide (SiC) is used at the side contacted to the optical recording layer as the protective layer of the optical recording layer including Ag, and ZnS or a compound including ZnS is used as the outer layer of the dielectric layer. The above SiN, SiC, AlN layer is used, thereby a combination of Ag included in the recording layer and S in the protective layer is prevented. As disclosed in Japanese Patent Application Laid-open No. 5-217211, a film thickness of the SiN, AMN, SiC layer is ranging from 5 nm to 50 nm. Furthermore, as disclosed in Japanese Patent Application Laid-open No. 6-195747, the protective layer has two layers inserted between the recording layer and the substrate, where one layer contacted to the recording layer comprises Si3N4 layer and the other layer contacted to the substrate comprises ZnSxe2x80x94SiO2 layer, thereby two dielectric layers are formed. The Si3N4 layer facilitates a crystallization of the phase change material layer.
The example of the optical magnetic recording medium is disclosed in Japanese Patent Application Laid-open No. 4-219650. Here, the dielectric layer contacted to the substrate has two layers, and one layer contacted to the substrate is a silicon oxide film, thereby an addhesiveness of the substrate and the dielectric layer is enhanced. Furthermore, the other layer contacted to the recording layer comprises the compound of the carbide and the nitride, thereby it is possible to prevent a corrosion of the magnetic recording layer occurred due to that oxygen from the silicon oxide layer and water passing through the substrate are penetrated into the recording layer. As disclosed in Japanese Patent Application Laid-open No. 4-219650, preferably, the nitride comprises Snxe2x80x94N, Inxe2x80x94N, Zrxe2x80x94N, Crxe2x80x94N, Alxe2x80x94N, Sixe2x80x94N, Taxe2x80x94N, Vxe2x80x94N, Nbxe2x80x94N, Moxe2x80x94N and Wxe2x80x94N, and the film thickness thereof is ranging from 10 nm to 20 nm. Furthermore, as disclosed in Japanese Patent Application Laid-open No. 4-321948, in the same view of Japanese Patent Application Laid-open No. 4-219650, the dielectric layer contacted to the substrate has two layers. Here, one layer near the substrate comprises at least one kind of oxides selected from a group of Si, Zr, Y, Mg, Ti, Ta, Ca and Al, thereby the adhesiveness of the dielectric layer and the substrate is enhanced. Furthermore, the other layer contacted to the optical magnetic recording film comprises the nitride layer comprising at least one kind of nitrides selected from the group of Si, Zr, Y, Mg, Ti, Ta, Ca and Al, thereby it is suppressed that oxygen and water from the oxide layer are penetrated and diffused into the recording film layer. As disclosed in Japanese Patent Application Laid-open No. 4-321948, the film thickness of the nitride layer is ranging from 50 nm to 200 nm.
It is known that the protective layer is formed of a complex material comprising different substances so as to provide the film with good quality. For example, Japanese Laid-Open Patent Publication (Tokkai-Sho) No. 63-50931 discloses an example including a protective layer with good quality such as excellent adhesiveness with a substrate by adding at least either one of aluminum oxide and silicon oxide to a complex dielectric of aluminum nitride and silicon nitride and by defining the refractive index.
Japanese Laid-Open Patent Publication (Tokkai-Hei) No.2-105351 discloses an example including a protective layer having excellent adhesiveness with a substrate and excellent ductility formed of a complex dielectric comprising a nitride of silicon and indium.
Furthermore, Japanese Laid-Open Patent Publication (Tokkai-Hei) Nos. 2-265051, 2-265052 disclose examples including a protective layer formed of Si, N and an element having a smaller specific electric resistance than Si, so that the protective layer is hardly cracked and protects the recording layer sufficiently.
In general, the reflecting layer 5 comprises a metal such as Au, Al, Cr, Ni, Ag or the like and the alloy based upon these metals, and the reflecting layer 5 is disposed in such a manner that a radiation effect and an effective optical absorption of the recording thin film can be obtained.
As described above, in general, a sputtering method, a vacuum deposition method or the like is used as the method of preparing the recording medium. Furthermore, a reactive sputtering method is used so that the nitride can be contained in the thin film.
For example, as the method of producing an ablation type write once medium, such a method that N is contained in the Te-containing recording layer by the reactive sputtering is disclosed in Japanese Patent Application Laid-open No. 63-151486. As disclosed in Japanese Patent Application Laid-open No. 63-151486, a mixed gas of Ar and nitride is discharged relative to a telluric selenium alloy target. After the recording film containing tellurium, selenium and nitride on the substrate is formed by the reactive sputtering method, a nitrogen gas is introduced, and a nitrogen plasma is generated, thereby a surface layer having a high nitrogen density than an inside of the recording layer is formed. The surface of the recording film is nitrided, thereby a weather-proofness and a sensitivity are enhanced, and further a power tolerance is increased. The nitrogen density of the nitride layer is ranging from 2% to 10%, preferably, it is ranging from 2% to 20%. Preferably, the thickness of the surface layer is ranging about from 1 nm to 10 nm.
Furthermore, the example of the ablation type recording material is also disclosed in Japanese Patent Application Laid-open No.63-63153. The target comprising a material containing Te and Se is sputtered in a nitriding-oxide gas, a nitric dioxide gas or a gas containing a nitric dioxide, thereby the layer containing Te, Se and N is formed in the recording layer.
Furthermore, as disclosed in Japanese Patent Application Laid-open No. 4-78032, the surface of a metallic target is sputtered by Ar gas, and on the surface of the metallic element substrate is reacted with oxygen gas or nitrogen gas, thereby a metallic oxide film or a metallic nitride film is formed.
Furthermore, although omitted in the drawings, in order that an oxidization of the optical information recording medium or an attachment of dusts, etc. is prevented, such a structure that the overcoat layer is placed on the metallic reflecting layer 5, such a structure that an ultraviolet curing resin is used as an adhesive so that a dummy substrate is laminated, or the like is proposed.
However, it is known that the phase change optical recording medium has the following problems. That is, when the thin film comprising a material whose base is Te, Se, etc. containing Ge, Sb, In, etc. is used as the recording layer, and further the thin film comprising an oxide system material including such as SiO2 representatively, the thin film comprising a sulfide system material including such as ZnS representatively, or the thin film comprising a mixture system material including ZnSxe2x80x94SiO2 between the above two thin films is used as the protective layer, a laser irradiation is carried out. Thereby, the record and erasure of the information signal, and the like are repeated, thereby optical characteristics of the recording layer and the protective layer (such as a reflectivity, an absorptivity and the like) are changed. Accordingly, such a phenomenon that a recording characteristic or an erasure characteristic is changed. That is, the signal is repeatedly rewritten, thereby the reflectance of the medium is reduced, an amplitude of the signal is gradually reduced, or a jitter value at a marked position of a recording mark becomes larger, thereby an error rate of the recording signal becomes higher. Therefore, when the signal is reproduced, a readout error is occurred. Accordingly, there is such a problem that a possible times of rewriting is limited.
Principal causes of this change are as follows. That is, one cause is that an S component and an O component are diffuse and penetrate from the protective layer to the recording layer, on the contrary, the component such as Te, Se, etc. having a relatively high vapor pressure among the components of which the recording layer consists of diffuse from the recording layer to the protective layer. Furthermore, another cause is that one part of the protective layer material is chemically reacted with the recording layer. It is considered that the change is occurred due to either of the above causes, or a combination of the above causes.
In fact, according to an experiment by inventors, etc., in the optical disk applying a Gexe2x80x94Sbxe2x80x94Te recording film and a ZnSxe2x80x94SiO2 protective layer, the S component is discharged from the protective layer due to the laser irradiation. Consequently, it is observed that an S atom is penetrated from the protective layer to the recording layer. Furthermore, it is also observed that the other Zn atom, Si atom and O atom are also diffused to the recording layer. In this case, although it is assumed that other elements are easy to move by a separation of the S atom, the mechanism thereof is not clear.
The phenomenon and the mechanism have not been clearly reported. In case that the nitride thin film including Si3N4 and AlN is used as the protective layer, the S component is not discharged, differently from the above example. On the other hand, an adherence to the recording layer of such a nitride is lower than that of ZnSxe2x80x94SiO2 film. For example, under an environment having a high temperature and a high humidity, there is another problem that a peeling is occurred. That is, when oxide such as SiO2, Ta2O5, Al2O3 and the like and nitride such as Sl3N4 AlN and the like are used as a dielectric material, since such a dielectric, material is less adhesive to a phase change type recording material, for example, under the high-temperature and high-humidity environment, the peeling and crack are occurred. Thereby, there is further problem that oxide such as SiO2, Ta2O5, Al2O3 and the like and nitride such as Si3N4, AlN and the like cannot be applied to a dielectric layer material.
A deterioration mechanism is summarized. In the first place, the more the times of repeating is increased, the more the above atom diffusion and chemical reaction are proceeded. Consequently, a composition in the recording layer is largely varied, thereby variations of the reflectance, the absorption and the like, and the variation of the recording characteristic (an amorphization sensitivity) and the erasure characteristic (a crystallization sensitivity and a crystallization rate) are actualized. It is supposed that in the protective layer, accompanied by the change of the optical characteristic, the composition changed, thereby such a change that a mechanical strength is reduced occurs. It can be considered a ZnSxe2x80x94SiO2 film widely applied as an excellent protective layer has a high adhesiveness between the protective layer and the recording layer and this results from the atomic diffusion. Furthermore, it is also considered that such a protective layer substantially contains a limit of the repeating times.
Relating to a material containing Ag and S, that is, the elements which are easy to chemically react, the method of suppressing the reaction is disclosed in Japanese Patent Application Laid-open No. 5-217211. However, the following view is not disclosed in the above prior art. That is, relative to the phase change recording medium such as Gexe2x80x94Sbxe2x80x94Te system, Inxe2x80x94Sbxe2x80x94Te system and the like being developed for an application as the most possible material system, in order to enhance the cycle performance thereof, the layer comprising the material such as nitride, nitriding-oxide, etc. is formed between a dielectric protective layer and a phase change recording layer. The formed layer acts as a barrier layer for preventing an interdiffusion and the chemical reaction between the recording layer and the protective layer. Furthermore, more specifically, Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O is superior as the dielectric protective layer material which does not substantially have the above problem. This material has also an excellent performance as the barrier layer. This is not also disclosed in the prior art.
That is, a layer structure for realizing an excellent repeating characteristic and an excellent weather-proofness is not yet achieved. In order to solve the above problems, it is an object of the present invention to provide a medium structure for realizing a phase change optical recording medium having the excellent repeating characteristic and weather-proofness, the producing method thereof, and a method of recording and reproducing an information signal by using the recording medium.
In order to solve above problems, according to one aspect of the present invention, there is provided an optical information recording medium comprising a recording layer generating a reversible phase change which can be optically detected according to an irradiation of an energy beam, and a material layer which is named a barrier layer formed in contact with at least one surface of the recording layer, wherein an atomic diffusion and a chemical reaction occurred between the protective layer and the recording layer are suppressed by the barrier layer.
A material constituting the barrier layer (a barrier material) itself can be applied to a protective layer material as it is. In this case, it is expressed as xe2x80x9cthe protective layer using the barrier materialxe2x80x9d.
According to another aspect of the present invention, preferably, there is provided an optical information recording medium, wherein a barrier material layer is disposed at both sides of a recording layer.
According to a structure in which the barrier material is applied to a substrate side of the recording layer, an effect for suppressing the atomic diffusion and the chemical reaction between the recording layer and the protective layer is higher, thereby a cycle performance is enhanced. According to the structure in which the barrier material is applied to the side opposite to the substrate of the recording layer, the effect for enhancing a stability of rewrite performance is higher, thereby a reliability is enhanced. Not only the structure in which the barrier material is applied to both sides of the recording layer combines both characteristics, but also both performances are further enhanced.
According to further aspect of the present invention, preferably, there is provided an optical information recording medium, wherein when the barrier material is represented by MaXb (where, M denotes an aggregate of non-gas elements M1, M2, . . . , and X denotes the aggregate of gas elements X1, X2, . . . ), regarding a ratio of a gas component b/(a+b), the ratio of the barrier material layer at the substrate side is relatively higher than that of the barrier material layer at the side opposite to the substrate.
According to further aspect of the present invention, preferably, there is provided an optical information recording medium further comprising a metallic reflecting layer.
According to further aspect of the present invention, preferably, there is provided an optical information recording medium, wherein the protective layer using the barrier materialxe2x80x9d having a thin thickness of 60 nm or less is applied between the metallic reflecting layer and the recording layer for a quenching. Thereby, since the number of layers can be reduced, a preparing process can be simplified. Furthermore, since a cooling effect is enhanced, thereby a thermal interference between recording marks is reduced, an information signal can be densely recorded. That is, the structure is advantageous to a high density recording. More preferably, in this case, the barrier layer is also applied to the substrate side of the recording layer. Thereby, it is possible to obtain the medium which can realize a higher cycle performance and a higher density recording.
According to further aspect of the present invention, preferably, there is provided an optical information recording medium, wherein xe2x80x9cthe structure (a rather slow cooling structure) necessary for a dielectric layer having a thickness of 80 nm or more between the metallic reflecting layer and the recording layer, the barrier layer is applied to at least one side of the recording layer. Thereby, usually, in the rather slow cooling structure having a tendency of high heat-storing effect and a large thermal damage, the cycle performance can be largely enhanced.
According to further aspect of the present invention, there is provided an optical information recording medium, wherein the thickness of the barrier layer is at least more than 1 nm to 2 nm. Thereby, the above effect can be obtained. Preferably, the thickness is 5 nm or more. Thereby, even if a laser power used for recording is higher, the effect can be obtained. Thereby, a further effect can be obtained. Furthermore, more preferably, the thickness is 20 nm or more. Thereby, a higher reproducibility can be obtained in preparing.
According to further aspect of the present invention, there is provided an optical information recording medium, wherein the barrier material layer containing Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O is used as the barrier material.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein when Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O material layer is applied at both sides of the recording layer as the barrier layer or the protective layer, regarding a density of a gas element in Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer, that is, (N+O)/(Ge+N+O), the density in Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer at the substrate side of the recording layer is relatively larger than that in Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer at the side opposite to the substrate of the recording layer.
According to further aspect of the resent invention, preferably there is provided an optical information recording medium, wherein Gexe2x80x94N composition region having a Ge density ranging from 35% to 90% is selected. More preferably, the range from 35% to 65% is selected.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein in case that the a Gexe2x80x94N layer is applied to the substrate side of the recording layer (at the side which a laser beam is incident on), the Ge density ranging from 35% to 60% is selected. In case that the Gexe2x80x94N layer is applied to the side opposite to the substrate of the recording layer, the Ge density ranging from 42.9% to 90% (preferably, 42.9% to 65%) is selected.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein in a triangular diagram in FIG. 5 showing three-element composition of Gexe2x80x94Nxe2x80x94O, Gexe2x80x94Nxe2x80x94O composition region is within a range surrounded by four composition points, B1(Ge90.0N10.0), B4(Ge83.4N3.30 O13.3), G4(Ge31.1 N13.8 O55.1), G1(Ge0.35 N0.65). In this region, there are such effects that the cycle performance is enhanced and an erasure performance is enhanced.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein in case that the Gexe2x80x94Nxe2x80x94O layer is applied to the substrate side of the recording layer (at the side which the laser beam is incident on), the region surrounded by four composition points D1(Ge60.0 N40.0), D4 (Ge48.8 N10.2 O41.0), G1 (Ge35.0 N65.0), G4(Ge31.1 N13.8 O55.1) is appropriate. In case that the Gexe2x80x94Nxe2x80x94O layer is applied to the side opposite to the substrate of the recording layer, the region surrounded by four composition points B1 (Ge65.0 N35.0), B4 (Ge54.3 N9.1 O36.6), F1 (Ge42.9 N57.1), F4 (Ge35.5 N12.9 O51.6) is appropriate. In this case, preferably, the region surrounded by four composition points C1 (Ge65.0 N35.0), C4 (Ge53.0 N9.2 O36.9), F1 (Ge42.9 N57.1), F4 (Ge35.5 N12.9 O51.6) is appropriate.
Similarly to the case of the Gexe2x80x94N layer, when the Gexe2x80x94Nxe2x80x94O layer is formed at the side opposite to the substrate of the recording layer (at the side which the laser beam is not incident on), in a process of recording and erasing, there is less possibility that a Ge atom is included in the recording layer. The layer can be also applied to the composition region having a considerably high Ge density. On the contrary, when the Gexe2x80x94Nxe2x80x94O layer is formed at the substrate side of the recording layer (at the side which the laser beam is incident on), there is more possibility that the Ge atom is included in the recording layer. It is not preferable that the layer is applied to the composition region having a considerably high Ge density.
As described above, the Gexe2x80x94N layer or the Gexe2x80x94Nxe2x80x94O layer is acted in such a manner that the atomic interdiffusion and chemical reaction generated between the recording layer and the protective layer usually comprising a dielectric material are suppressed. There is such an advantage that the Gexe2x80x94N layer or the Gexe2x80x94Nxe2x80x94O layer has a higher adhesiveness to the recording layer, compared to other nitride films such as Si3N4, AlN, etc. and a carbide film such as SiC, etc. The reason that the Gexe2x80x94N layer or the Gexe2x80x94Nxe2x80x94O layer has a higher adhesiveness is as follows. Compared to other nitride films such as Si3N4, AlN, etc., the Gexe2x80x94N layer or the Gexe2x80x94Nxe2x80x94O layer enables to form the film with a relatively lower power at a high speed (for example, when a distance between a target and the substrate is 200 mm, if the target whose diameter is 100 mm is used, the film can be formed with 500 W at 40 nm to 50 nm/minute). Accordingly, it is assumed that since an internal stress in the film is lower, the Gexe2x80x94N layer or the Gexe2x80x94Nxe2x80x94O layer has a higher adhesiveness. However, this is not clear.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein a complex refractive index value n+ik applies the Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer satisfying the range of 1.7xe2x89xa6nxe2x89xa63.8 and 0xe2x89xa6kxe2x89xa60.8. More preferably, when the barrier material layer is formed at the substrate side of the recording layer, the Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer satisfying the range of 1.7xe2x89xa6nxe2x89xa62.8 and 0xe2x89xa6kxe2x89xa60.3 is applied. When the barrier material layer is formed at the side opposite to the substrate, the Gexe2x80x94N or Gexe2x80x94Nxe2x80x94O layer satisfying the range of 1.7xe2x89xa6nxe2x89xa63.8 and 0xe2x89xa6kxe2x89xa60.8 is applied. An optical constant is changed according to a ratio of O to N in the film, when O is less, the optical constant becomes larger. When O is more, the optical constant becomes smaller.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein a material thin film whose main component is Gexe2x80x94Sbxe2x80x94Te is used as the recording layer.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein the material thin film whose main component is ZnSxe2x80x94SiO2 is used as a dielectric protective layer material used together with the barrier layer.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein a material layer containing a main component comprising a nitride or a nitriding-oxide having at least one kind of element selected from the elements constituting the recording layer is used as the barrier material layer.
In general, although a nitride material is less adhesive to a chalcogenite material, the barrier layer containing a nitride or nitriding-oxide of the element included in the recording layer is used, thereby the elements in the barrier layer is common to the component element in the recording layer. Accordingly, the adhesiveness can be enhanced. In this case, it is possible to suppress the interdiffusion and the chemical reaction between the recording layer and the protective layer whose main component is the dielectric material. Thereby, the phase change optical recording medium having the excellent repeating performance and excellent weather-proofness can be realized.
According to further aspect of the present invention, preferably there is provided an optical information recording medium, wherein at least one surface of the recording layer is nitrided or nitric-oxidized, thereby the barrier layer is formed.
In this case, since the recording layer and the nitride layer or the nitric-layer have the films having a high continuity to each other, there is less problem relating to the adhesiveness. Accordingly, the optical information recording medium having the excellent repeating performance and the excellent weather-proofness can be obtained.
According to further aspect of the present invention, a method of preparing an optical information recording medium for solving the above problems, comprising a vacuum deposition method, a DC sputtering method, a magnetron sputtering method, a laser sputtering method, an ion plating method, a CVD method and the like.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein a sputtering method is used, a single target comprising the main component M of the barrier material, a nitride target comprising M, a nitric-oxide target, or an oxide target is used in order that the barrier material layer is formed, so that a reactive sputtering is carried out in a mixed gas of a rare gas and the gas containing a nitride component or the mixed gas of the gas containing the rare gas and the nitride component and the gas containing an oxide component, thereby the barrier material layer is formed.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein Ar and Kr are used as the rare gas.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein N2 is used as the gas containing the nitride component, and O2 is used as the gas containing the oxide component.
When the barrier material layer is formed at either sides of the recording layer, an N2 density in case that the barrier material layer is formed at the side opposite to the substrate of the recording layer is highly set than that in case that the barrier material layer is formed at the substrate side of the recording layer. Thereby, the structure having a further higher weather-proofness can be obtained.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein Ge is used as the main component M of the barrier material, a Ge target, a Gexe2x80x94N target, a Gexe2x80x94Nxe2x80x94O target or a Gexe2x80x94O target is used so that the reactive sputtering is carried out, thereby the barrier material layer is formed. More preferably, a Ge3N4 composition is used as the Gexe2x80x94N target, a GeO composition is used as the Gexe2x80x94O target, and Ge3N4xe2x80x94GeO mixed target is used as the Gexe2x80x94Oxe2x80x94N target. According to further aspect of the present invention, a method of preparing an optical information recording medium, more preferably, wherein Ge is used as the main component M of the barrier material, when the reactive sputtering is carried out, a total pressure of a sputter gas is more than 1 mTorr, and it is 50 mTorr or less. Within this range, a high sputter rate and a stable discharge can be obtained.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein Ge is used as the main component M of the barrier material, when the reactive sputtering is carried out, the sputter gas is the mixed gas containing at least Ar and N2, a partial pressure ratio of N2 is ranging from 5% to 60%. Thereby, a better repeating performance and a better weather-proofness can be obtained. In this case, when the barrier layer is used at the substrate side of the recording layer, the partial pressure ratio of N2 is ranging from 12% to 60% (preferably, 50% or less). Furthermore, when the barrier layer is used at the side opposite to the substrate, the partial pressure ratio of N2 is ranging from 5% to 60% (preferably, 40% or less, more preferably, 33% or less).
Regarding the repeating performance, when a nitride partial pressure in the sputter gas is low, since much surplus Ge not combined to a nitrogen exists in the protective layer, the composition in the recording film is changed, accompanied with rewriting the signal, thereby a better characteristic cannot be obtained. Furthermore, when the nitrogen partial pressure in the sputter gas gets too high, much surplus nitrogen exists in the film, thereby similarly to the above case, the better repeating characteristic cannot be obtained.
Regarding the weather-proofness (adhesiveness), when the nitrogen partial pressure in the sputter gas is high and much surplus nitrogen exists in the film, after an acceleration test, a peeling is occurred. However, when the nitrogen partial pressure is low and the surplus Ge not combined to the nitrogen exists, the peeling is not occurred. It is assumed that since Ge contributes to a combination with the recording film, the peeling is not occurred.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein Ge is used as the main component M of the barrier material, when the reactive sputtering is carried out, the sputter gas is the mixed gas containing at least Ar and N2 a sputter power density is more than 1.27 W/cm2, and a film forming rate is 18 nm/minute or more.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein Ge is used as the main component M of the barrier material, when the reactive sputtering is carried out, the sputter gas is the mixed gas containing at least Ar and N2 the film is formed in such a manner that the complex refractive index value n+ik may satisfy the range 1.7xe2x89xa6nxe2x89xa63.8, 0xe2x89xa6kxe2x89xa60.8. More specifically, when the barrier material layer is formed at the substrate side of the recording layer, such a film forming condition as to satisfy the range 1.7xe2x89xa6nxe2x89xa62.8, 0xe2x89xa6kxe2x89xa60.3 is selected. When the barrier material layer is formed at the side opposite to the substrate, such a film forming condition as to satisfy the range 1.7xe2x89xa6nxe2x89xa63.8, 0xe2x89xa6kxe2x89xa60.8 is selected.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein at least one element among the materials constituting the recording layer is used as the main component of the barrier material layer, its single element target, its nitride target, its nitriding-oxide target or its oxide target is used, so that the reactive sputtering is carried out in the mixed gas of the rare gas and the gas containing the nitrogen component or the mixed gas of the rare gas and the gas containing the nitrogen component and the gas containing the oxygen component, thereby the film is formed.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein the material itself constituting the recording layer is used as it is as the main component of the barrier material layer, the target for forming the recording layer, its nitride target, its nitriding-oxide target, or its oxide target is used, so that the reactive sputtering is carried out the mixed gas of the rare gas and the gas containing the nitrogen component or in the mixed gas of the rare gas, the gas containing the nitrogen component and the gas containing the oxygen component, thereby the film is formed.
According to further aspect of the present invention, a method of preparing an optical information recording medium, preferably, wherein the material itself constituting the recording layer is used as it is as the main component of the barrier material layer, in at least either a recording layer formation start time or a recording layer formation completion time, either a process of forming the recording layer in which the density of the gas containing the nitride component in the sputter gas is enhanced, or a process of forming the recording layer in which the densities of the gas containing the nitride component and the gas containing the oxide component are enhanced is used, thereby the recording layer formation can be achieved.
According to the above processes, a supply of the gas constituting the nitride component and the oxide component may be stopped when a recording layer portion is formed in the recording layer formation process.
An optical information recording medium of one embodiment in the present invention includes a barrier layer, a first protective layer, and a recording layer generating a reversible phase-change which can be optically detected according to an irradiation of an energy beam. The barrier layer is formed between the first protective layer and the recording layer and in contact with the first protective layer and the recording layer. The barrier layer includes either one selected from the group consisting of GeN and GeNO, and at least one element selected from the group consisting of Al, B, Ba, Bi, C, Ca, Ce, Cr, Dy, Eu, Ga, H, In, K, La, Mn, N, Nb, Ni, Pb, Pd, S, Si, Sb, Sn, Ta, Te, Ti, V, W, Yb, Zn and Zr.
In an optical information recording medium of another embodiment in the present invention, the barrier layer is formed between the first protective layer and the recording layer and in contact with the first protective layer and the recording layer. The barrier layer is composed of a barrier material having a non-stoichiometric composition.
An optical information recording medium of one embodiment in the present invention includes a recording layer having reversibly changeable optical characteristics and a Ge-containing layer comprising either one selected from the group consisting of GeXN and GeXON as a main component, where X is at least one element selected from the group consisting of elements belonging to Groups IIIa, IVa, Va, VIa, VIIa, VIII, Ib and IIb and C. This makes it possible to provide a medium having excellent weather resistance and excellent characteristics in repetitive recording.
According to another aspect of the present invention, a method for producing an optical information recording medium includes the steps of: forming a recording layer having reversibly changeable optical characteristics, and forming a Ge-containing layer comprising either one selected from the group consisting of GeXN and GeXON as a main component, where X is an element as described above. The Ge-containing layer is produced by reactive sputtering with a target including at least Ge and X in a mixed gas comprising a rare gas and nitrogen. This makes it possible to produce efficiently an optical information recording medium having excellent weather resistance and excellent characteristics in repetitive recording.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.